Many ophthalmic surgical procedures require illuminating a portion of a patient's eye so that a surgeon can observe the surgical site. Various different types of instruments are known and available for use by an ophthalmic surgeon to illuminate the interior of the eye. The handheld (probe) portion of a typical ophthalmic illuminator comprises a handle having a projecting tip and a length of optical fiber that enters a proximal end of the handle and passes through the handle and the tip to a distal end of the tip, from which light traveling along the optical fiber can project. The proximal end of the optical fiber can be positioned adjacent to a light source, such as in a high brightness illuminator, as known to those having skill in the art, to provide the light that is transmitted through the fiber. These types of handheld illuminators are typically used by inserting the probe tip through a small incision in the eye. In this way, light from the illuminator light source is carried along the optical fiber, through the handpiece and emitted from the distal end of the probe (fiber) to illuminate the surgical site for the surgeon. Ophthalmic illuminators that use a length of optical fiber to carry and direct light from a light source to a surgical site are well known in the art.
Such an ophthalmic illumination system typically comprises a handheld portion, or probe, to deliver illumination from a light source housed in an enclosure, the enclosure typically housing the light source and associated optics that guide light from the light source to the optical fiber of the probe, a power supply, electronics with signal processing, and associated connectors, displays and other interfaces as known in the art. While some ophthalmic illumination systems use other types of lamps as a light source, a preferred light source is a xenon lamp. Some prior art xenon lamps exists that use quartz for the lamp body material. However, quartz has been found to be unstable at the high operating temperature of typical xenon lamps and has a tendency to fail and sometimes explode. This is because as the quartz lamp body ages, the quartz crystallizes, cracks, and is then susceptible to failure. As a result, these prior art xenon lamp illuminators contain the xenon lamp and quartz lamp body within a steel housing. Ceramic lamp bodies, on the other hand, have been found safe for use in the high temperature environment of a xenon lamp. Most modern ophthalmic illumination systems using xenon lamps thus typically employ a ceramic body.
However, unlike with a quartz lamp body, the electrodes of a ceramic-bodied xenon lamp typically intrude into the lamp's optical path. This disadvantage is not present in prior art quartz-bodied lamps because the lamp electrodes are vertical and do not invade into the optical path. However, in a ceramic body, the electrodes are placed such that they interfere with the center portion of the lamp's optical beam, resulting in a “donut” shaped optical beam instead of a more homogenous “dot-shaped” beam. The reflector, electrodes and their associated supports cast shadows within the optical beam resulting in a focal spot having a donut shape, as shown in FIG. 1.
The annular-shaped focal spot of ceramic-bodied high-pressure xenon lamps has until recently not been a problem for ophthalmic illumination systems because these prior art systems typically use fiber bundles (e.g., 3 to 6 mm fiber bundles) to receive the annular focal spot and transmit the received light from the light source to a surgical site. However, with the advent of small core-diameter optical fibers (e.g., about 3 mm diameter) such as can be used with the Alcon High Brightness Illuminator, manufactured by Alcon Laboratories, Inc., of Irvine, Calif., for use in ophthalmic endo-illumination systems, the annular focal spot of prior art xenon lamps is in conflict with the desire to couple the xenon lamp output into a small core optical fiber. This is particularly so because these modern endo-illuminators typically use a single fiber to guide and direct light from the light source to the surgical site. Such small core optical fiber endo-illuminators are desirable because they require a smaller incision and thus lessen trauma and possible damage to a patient's eye.
Focusing the output from a xenon light source in these prior art ophthalmic illumination systems into a small core diameter optical fiber is thus not only difficult, but results in a poor optical-coupling to the optical fiber. Further, the annular focal spot from such an illuminator is typically approximately 1 mm in diameter. Focusing this annular focal spot into an approximately half a millimeter fiber (e.g., a typical 25-gauge optical fiber) results in an irregular intensity distribution of the transmitted light. Note that for a 20 gauge optical fiber the problem is not as great because the entire annular focal spot can fit within the 20-gauge optical fiber diameter.
Prior art ophthalmic illumination systems have attempted to solve this problem by defocusing the annular focal spot to direct some light into the central portion of the focal spot. The problem with this approach is that as the focal spot is defocused, the intensity of the transmitted light decreases because less of the light from the light source is directed into the optical fibers. Further, although prior art ophthalmic illumination systems do not focus the output of the xenon lamp into a single optical fiber, when focusing the output of the xenon lamp into a fiber bundle, prior art illuminators have attempted to beam-shape the output of the xenon lamp by the use of diffractive optical elements. The problem with the use of diffractive elements is that they are sensitive to changes in the light source beam, and the output from a xenon lamp changes significantly as the lamp ages. Also, inexpensive custom-made diffractive elements are typically made of plastic, which can be damaged relatively easily by a high intensity optical beam originating at a xenon lamp.
Therefore, a need exists for a method and system for correcting an optical beam that can shape the annular focal spot pattern from a high pressure ceramic xenon lamp into a focal spot with quasi-Gaussian intensity distribution for efficient optical fiber coupling. Further still, there is a need for such a method and system for correcting an optical beam that will provide stable correction as a lamp source ages and that can improve fiber coupling efficiency of the lamp source output into a small (e.g., ≦3 mm diameter) optical fiber, such as 20 and 25 gauge optical fibers.